000 AXNT20 KNHC 021801 TWDAT Tropical Weather Discussion NWS National Hurricane Center Miami FL 201 PM EDT Wed Aug 2 2017 Tropical Weather Discussion for North America, Central America Gulf of Mexico, Caribbean Sea, northern sections of South America, and Atlantic Ocean to the African coast from the Equator to 32N. The following information is based on satellite imagery, weather observations, radar and meteorological analysis. Based on 1200 UTC surface analysis and satellite imagery through 1745 UTC. ...TROPICAL WAVES... An eastern Atlantic tropical wave extends its axis from 18N34W to 14N35W to 06N35W, moving west at 10-15 kt. Dry Saharan air surrounding this wave's environment is suppressing deep convection from developing along or near it. The northern portion of the wave appears to be tilting to the northeast as suggested by the 700 mb streamline guidance from the GFS model. Isolated showers are possible near where the wave crosses the monsoon trough. A central Atlantic broad tropical wave extends its axis from 22N60W to 15N60W to inland South America at 06N59W, moving west at 15-20 kt. The CIMSS total precipitable water imagery (TPW) animation shows an extensive area of very deep moisture trailing the wave to near 50W from 10N-15N. Scattered moderate isolated strong convection in clusters is within this area of moisture. This activity is likely attendant by strong gusty winds. Similar activity precedes the wave into the eastern Caribbean to near 64W, and is also likely to contain strong gusty winds as it quickly moves westward. Wind gusts to 30-35 kt were reported this morning in some of the Leeward Island locations. Fresh to locally strong east to southeast winds will follow in behind the wave as it moves across the eastern Caribbean through Friday. The Saharan Air Layer imagery shows dry air and dust to the north and northeast of the deep moisture area that follows the wave. A western Caribbean tropical wave extends its axis from 19N84W to inland eastern Honduras and continues south-southeast to the eastern portions of Nicaragua and Costa Rica. The CIMSS TPW shows very deep moisture within 120 nm east of the south of 15N. Scattered moderate isolated strong convection is within this moisture area. Isolated showers and thunderstorms are within 60 nm either side of the wave axis north of 15N. The scattered moderate isolated strong convection is forecast to spread inland Honduras, Costa Rica and Panama through this evening. ...ITCZ/MONSOON TROUGH... The monsoon trough axis extends from the coast of African near 14N16W to 10N26W to 11N39W to 11N48W, where scatterometer data indicates the ITCZ begins and continues to 11N59W. Scattered moderate isolated strong convection is within 120 nm south of the monsoon trough between 43W-45W. Scattered moderate convection is within 240 nm south of the monsoon trough between 20W-25W, within 120 nm south of the trough between 38W-43W, and well south of the monsoon trough within 30 nm either side of line from 08N15W to 07N20W. Scattered moderate to strong convection is inland and off the coast of Africa from 07N-11N. This activity is ahead of the next tropical wave that is expected to emerge off the coast of Africa in the near future. ...DISCUSSION... GULF OF MEXICO... A surface trough is analyzed from NE Florida southwest to just north of Tampa, and continues southwest to a 1014 mb low at 28N86W and southwest to near 26N91W. A 1016 mb small low recently formed just offshore the northern Florida coast near 29.5N83W as of 15Z. In the upper levels, very strong westerly winds are evident north of 29N, while moderate to strong north to northeast winds around the eastern periphery of a large upper anticyclone centered over far northern Mexico are to the south of 29N. The resultant speed diffluence is helping to support scattered moderate isolated strong convection over the eastern Gulf from 26N-29N east of the 1014 mb. Scattered moderate convection has recently developed over the western Gulf within 30 nm of 26N94W, and within 60 nm of 29N93W. Scattered showers and isolated thunderstorms are elsewhere north of 25N, while isolated showers and thunderstorms are south of 25N. A thermal trough moved offshore the Yucatan Peninsula last night, and is along 93W/94W south of 22N. Isolated showers are possible within 30-60 nm of the trough. Scatterometer data depicts a light to gentle cyclonic flow across the basin, with higher speeds in and near the convection near the aforementioned lows. Expect for the surface trough to drift north over the next 24 hours with convection. The surface low near 28N86W is expected to drift northeastward through tonight while gradually dissipating into Thursday morning. The low just offshore the northern Florida coast will move inland this afternoon. The surface trough will slowly lift northward and weaken through Thursday night in response to an upper trough that digs southward over the central U.S. Unsettled weather is expected through Friday over much of the central and eastern Gulf. CARIBBEAN SEA... A tropical wave is moving across the far western Caribbean. See the section above for details. Isolated showers are noted over the western half of Cuba and the Yucatan Channel. Scattered moderate isolated strong convection in clusters cover much of the central and eastern Caribbean between 64W-76W. This activity has significantly increased since yesterday, and is being supported marginal speed diffluence aloft that is occurring on the southern periphery of an upper anticyclone centered just north of the Mona Passage. An inverted mid-upper level troughs near 66W and 74W are helping to provide additional instability and support to this activity as it quickly moves westward. The activity will spread across the rest of the central Caribbean through tonight and the western Caribbean Thursday through Friday. A tropical wave is just east of the Lesser Antilles, and is preceded by similar convection as what is currently being observed over the central Caribbean. This convection reaches westward to near 64W, and is expected to spread westward over the eastern Caribbean through Thursday. The pressure gradient associated with sub-tropical Atlantic high will support fresh to strong winds across the north-central Caribbean Sea and Windward Passage through Saturday. Little change is expected elsewhere. ...HISPANIOLA... Scattered to locally broken low clouds with developing isolated showers and thunderstorms are over the interior of the central portion of the Dominican Republic, and over some locations in Haiti, mainly the northern and southern sections. As the afternoon wears on and daytime heating becomes prolonged, expect for shower and thunderstorm activity to increase over some of the interior locations. Scattered showers and thunderstorms over much of the central and eastern Caribbean are expected to stay south of Hispaniola, for the most part, but some may approach or move over the southern section of the island this evening and through much of Thursday. ATLANTIC OCEAN... Two tropical waves are moving across the Atlantic basin. The one along 60W will cross into the eastern Caribbean Sea this afternoon. See the sections above for details. The southern portion of an upper trough extends from near 32N77W to the central and NW Bahamas. Scattered showers and thunderstorms are east of the trough north of 28N between 67W-75W. Other scattered shower and thunderstorm activity is just inland and along the coast of NE Florida. The remainder of the basin is under the influence of a surface ridge, anchored by a 1026 mb high centered north of the area near 34N25W, another 1026 mb high at 32N40W and a 1025 mb high at 30N56W. Generally dry and stable conditions under the influence of the Saharan Air layer are present elsewhere east of about 70W and north of the tropical waves. The Saharan Air Layer is more evident over the central and eastern portions of the basin. Scattered showers and thunderstorms are expected to remain active over the northwest portion through Thursday night. For additional information please visit http://www.hurricanes.gov/marine $$ Aguirre